1. Technical Field of the Invention
The present invention relates to a rotational damper and a vehicle seat with the rotational damper that adds a predetermined braking force to a controlled object, which performs a rotating motion, such as a vehicle seat to buffer the rotating motion.
2. Description of the Related Art
As a vehicle seat for automobiles or the like are, as shown in FIG. 31, a reclining device, which is mainly mounted on a front seat 4 side, for connecting a seat cushion (seat side) 1 and a seat back (back side) 2 with each other by a hinge mechanism 3 and making the seat back 2 tiltable at a predetermined angle in a longitudinal direction of the vehicle to fix the seat back 2 at a desired tilt angle, and a double fall-down seat, which is mainly mounted on a rear seat 8 side, in which a seat cushion 1A is connected to a hinge mechanism 6 fixed to the vehicle body floor 5 at a forward lower portion thereof, and the seat cushion 1A is risen substantially 90 degree as indicated by chain lines 1A1 with the hinge mechanism 6 as a supporting point, further the seat cushion 1A is inverted 180 degree upside down as indicated by chain lines 1A2, and a seat back 2A, which is connected to a hinge mechanism 7 fixed to the vehicle body floor 5, is risen substantially 90 degree, or folding the seat back 2A forward into a space position of the seat cushion 1A that is inverted substantially 180 degree upside down as indicated by chain lines 2A1 to widen a luggage's space, and further a single fall-down seat in which a seat back 2A, which is connected to the hinge mechanism 7 fixed to the vehicle body floor 5, is pushed forward on the seat cushion 1A side.
Meanwhile, releasing fixation of the seat back 2 or 2A that is in standing position causes the seat back 2 or 2A to rapidly rotate and tilt forward due to urging force of a return spring (spiral spring) mounted to the hinge mechanism 3 or 7, and when the seat cushion 1A is inverted about 180 degree upside down from a standing position of about at 90 degree, the seat cushion 1A rapidly rotates and tilts due to urging force of a return spring disposed in the hinge mechanism 6. For instance, releasing the fixation of the seat back 2 or 2A when infants seat thereon as they are may cause large damage to the infants, such as catching of their bodies, or there may be damages of articles laid on the seat cushion 1 or 1A.
To solve the above problems, conventionally, it is proposed a construction in which a rotating damper (rotational damper) that acts to add a predetermined braking force to a controlled object such as a seat back of a vehicle seat and so on with rotational motion and to make the rotational motion thereof to be slow, which prevents rapid rotation and tilting of the controlled objects, is mounted to the above hinge mechanism, or a construction in which an oil damper or an air damper is mounted between a seat cushion and a seat back (Patent documents 6 and 7).
The rotational damper mounted to the hinge mechanism generates fluid resistance force by rotation of vanes (rotary vanes), which are disposed in a fluid chamber (casing) in which viscous fluid is stored. As these rotational dampers, there are one way rotational dampers (Patent documents 1 to 5) having a check valve such that vanes thereof provide braking force only in one way, and bidirectional rotational dampers that are constructed without a check valve and can provide braking forces regardless of rotational direction.
In this kind of rotational damper, fluid resistance force that is generated when fluid pressed by rotation of vanes flows through a small gap between the vanes and an inner peripheral wall of a fluid chamber makes rotational movement of a controlled object slow to avoid shocking contact to fixed members of the controlled object.
Therefore, magnitude of the braking force provided by the rotational dampers can be changed by making the gap through which the viscous fluid flows changeable. More specifically, the larger the gap through which viscous fluid flows is made, the smaller the fluid resistance of the viscous fluid becomes, so that braking force can be smaller, and the smaller the gap through which viscous fluid flows is made, the larger the fluid resistance of the viscous fluid becomes, resulting in larger braking force.
Patent document 1: Japanese Patent Publication No. 2006-242318 gazette
Patent document 2: Japanese Patent Publication No. Heisei 4-282039 gazette
Patent document 3: Japanese Patent Publication No. Heisei 5-52228 gazette
Patent document 4: Japanese Patent Publication Heisei 5-263847 gazette
Patent document 5: Japanese Patent Publication No. Heisei 7-301272 gazette
Patent document 6: Japanese Utility Model Publication No. Heisei 5-34940 gazette
Patent document 7: Japanese Utility Model Publication No. Heisei 7-265148 gazette
In the damper disclosed in the above Patent document 1, there is a problem that unless a rotor main body, pieces of a vane, and a control valve relatively largely shift in positions in relation to each other a switching passage through which viscous fluid flows does not open and close. In addition, in the dampers disclosed in the Patent documents 2 to 5, a pair of vanes are attached to a rotor so as to radially extend from the rotor; a control valve is formed to have C-shaped cross section; and movement of the control valve is made large to constitute an one-way damper, so that a migration length of the control valve to the vane becomes long when switching from braking condition to non-braking condition or from non-braking condition to braking condition, resulting in poor response.
The present invention has been made in consideration of the above circumstances, and the object thereof is to provide a rotational damper and a vehicle seat with the rotational damper for exerting braking action only in one direction with excellent response.